An optical disc 1 for storing data is configured as shown in FIG. 1. Data are recorded along spiral tracks 10, starting from the center of the optical disc 1 and ending at 5 mm from the edge of the optical disc 1.
For accessing data, the optical disc rotates and an optical head of the optical drive moves through the tracks of the optical disc. The optical disc may be rotated according to different control strategies. One of the control strategies to rotate the optical disc is so-called as a CAV (Constant Angular Velocity) method. The CAV method is commonly used in low-speed optical disc. According to the CAV method, the rotating angle per second is fixed, so the RPM (Round per Minute) of the optical disc is fixed as well.
Another strategy for controlling the rotation of an optical disc is a CLV (Constant Linear Velocity) method. The CLV method is advantageous to keep the data flow constant either in inner tracks or outer tracks. According to the CLV method, the data is read or written at a constant rate. For example, data can be read at a transmission speed of 300K per second by the CLV method. For achieving the purpose of constant read/write rate, the spindle motor of the optical disc for rotating the optical disc needs to change speeds all the time. The inner the track to be read, the higher the rotating speed of the spindle motor. Aside from the CLV method, the rotating speed of the spindle motor needs changing frequently in other non-CAV methods.
On the other hand, the optical head needs to move for seeking or jumping among tracks, as illustrated in FIG. 2. When an optical head 20 of an optical disc 2 is to move inwards for seeking tracks, e.g. move from an outer track 21 to an inner track 22, a certain level of power needs to be supplied to an actuator (not shown) to move a sled 201 where the optical head 20 is seated. Meanwhile, more and more power needs to be supplied to a spindle motor 23 for rotating the optical disc from the outer track 21 to the inner track 22 under the CLV control or non-CAV control. Therefore, undesired current spikes may occur on the power supply.